The expected values of Kirchhoff indices in the random polyphenyl and spiro chains

Abstract

The Kirchhoff index Kf(G) of a graph G is the sum of resistance distances between all pairs of vertices in G. In this paper, we obtain exact formulas for the expected values of the Kirchhoff indices of the random polyphenyl and spiro chains, which are graphs of a class of unbranched multispiro molecules and polycyclic aromatic hydrocarbons. Moreover, we obtain a relation between the expected values of the Kirchhoff indices of a random polyphenyl and its random hexagonal squeeze, and the average values for the Kirchhoff indices of all polyphenyl chains and all spiro chains with n hexagons, respectively.